In respect of miniaturization, a multilayer ceramic body offers the advantage that electrical components, for example interconnections, resistors, capacitors and inductors can be integrated in its volume. Known production methods are HTCC (high temperature cofired ceramics) and LTCC (low temperature cofired ceramics) technologies. In these technologies, unsintered ceramic green sheets are provided with through-contacts and planar conduction structures using metal-filled electrically conductive pastes by the stamping and screen printing methods and subsequently sintered together in a stack. This creates heatable, hermetically sealed multilayer planar substrates. These multilayer substrates can function as circuit supports of further components. The advantage of LTCC technology is that the firing temperature for sealing is so low that highly electrically conductive metals which melt at relatively low temperature, such as silver or copper, can be used for integration of the components.
For many fields of application, for example current and voltage transformation or lowpass filters in power electronic circuits, inductive components with better magnetic coupling are required, based on magnetic materials which can amplify and shape the magnetic flux, owing to the lower frequencies (in the MHz range). Many variants of coil and transformer cores made of ferritic ceramic are available for this, which can be fastened afterwards with the aid of metal clips on the aforementioned planar circuit supports.
It has not yet been possible to establish the integration of such inductive components owing to the disparate demands on material and process technology. Above all, two problems are encountered:                According to experience, increasing the magnetic performance of ferrites i.e. increasing the permeability of the core material, with the aid of ceramic technologies, entails a decrease in the resistivity of the core material and therefore a reduction of the important DC isolation between the primary and secondary sides of the transformer.        If current windings are embedded homogeneously in ferrite material, then some magnetic field lines may be closed on shorter paths without contributing to the magnetic coupling of the turns; such stray inductances reduce the performance of the inductive component.        
Both difficulties may in principle be resolved by embedding the current-carrying turns in highly insulating material with low permeability. Such a solution is known from U.S. Pat. No. 5,349,743 A. This discloses a method for producing a monolithic multilayer ceramic body with an integrated transformer. LTCC technology is employed, using a low-permeability material with a relatively high electrical resistivity and a higher-permeability material with a relatively low resistivity. These two materials are integrated by stamping out openings in the green sheets of one material, filling the openings with sheet portions or sheet stacks of the other material, and subsequently sintering them together. This process, which inherently involves lateral structuring of green sheets, is elaborate and relatively expensive.